Vitamin B3 (niacin) test: what the result means

Niacin (vitamin B3) is a water-soluble vitamin that the body does not store in large amounts — it needs to be taken in constantly with food or, in rarer cases, the body makes it from the amino acid tryptophan. Niacin takes part in the working of the digestive system, the skin and the nerves, and helps turn food into energy. It is found in milk, eggs, enriched bread and cereals, rice, fish, lean meat, legumes and nuts. A blood test for niacin is done infrequently — most often together with other B-group vitamins, when a general deficiency of these vitamins is suspected. The most striking and best described consequence of long-term niacin deficiency is pellagra — a disease that shows up as digestive problems, inflammation of the skin in sun-exposed areas and changes in mental function. Because niacin is water-soluble, an excess from food is usually removed in the urine, but large amounts from supplements can cause unwanted effects. Niacin status is often assessed together with overall nutrition and other B-group vitamins.

• When there are symptoms pointing to a possible deficiency of B-group vitamins (including B3) — weakness, digestive problems, skin changes
• When pellagra is suspected — with inflammation of the skin in sun-exposed areas, diarrhoea and changes in mental function
• In people who misuse alcohol over a long time — because of the increased risk of niacin deficiency
• After bariatric (stomach reduction) surgery, or in digestive tract diseases that interfere with absorption
• In anorexia, or where there is another sign of long-term inadequate nutrition
• In people taking large amounts of niacin supplements — to watch for a possible excess

We do not give a numeric reference range for vitamin B3 here: an exact, widely published numeric interval could not be reliably confirmed in the MedlinePlus sources we use. You will find the exact interval used by your laboratory on your own result sheet — see also how to read blood test results.

A raised niacin level is most often linked to large amounts from supplements rather than to food — niacin from food is water-soluble, and an excess is usually removed in the urine. Per MedlinePlus, excessive amounts of niacin can cause flushing of the skin, a raised blood glucose level, liver damage and peptic ulcer.

Causes listed for a high result:

• Taking large amounts of niacin (nicotinic acid or nicotinamide) supplements
• Long-term use of large supplement doses without a doctor's supervision

Possible symptoms:

• Flushing of the skin — a feeling of warmth, redness, itching or tingling
• Skin rashes
• A raised glucose (sugar) level in the blood
• Peptic ulcer

What is usually looked at after a high result:

• Which supplements are being taken and in what amounts — worth discussing with your doctor
• Liver markers, if large amounts of niacin supplements are taken over a long time
• The glucose level in the blood, especially if risk factors are already present
• Whether the symptoms (flushing, rash) are connected with the timing of the supplement

A low niacin result (deficiency)

A lowered niacin level over time causes pellagra — a disease that shows up as digestive problems, inflammation of the skin and changes in mental function. Per MedlinePlus, pellagra is most often linked to a poor diet, to alcoholism, or to conditions that interfere with the absorption of niacin or tryptophan.

Causes listed for a low result:

• Not enough niacin or tryptophan in food (especially when the main food source is unprocessed maize)
• Digestive tract disease or bariatric surgery that interferes with absorption
• Long-term alcohol use
• Anorexia or another sign of long-term inadequate nutrition
• Carcinoid syndrome
• Some medicines that affect niacin metabolism

Possible symptoms:

• Changes in mental function, confusion
• Diarrhoea
• Weakness, loss of appetite
• Abdominal pain
• Inflamed mucous membranes
• Scaly skin with sores, especially in sun-exposed areas

What is usually looked at after a low result:

• Diet and its variety — whether enough protein-rich food and B-group vitamins are being taken in
• Alcohol drinking habits
• Digestive tract conditions or operations that could interfere with absorption
• Whether there is a deficiency of other B-group vitamins — these are often assessed together